Two tales about companionship mark the highly propitious start of a new series. The gentle, affecting first volume introduces elderly Mr. Putter, who decides that a cat will keep him from feeling lonely. Only kittens are available at the pet store (`` `Oh, no one wants cats, sir,' said the pet store lady. `They are not cute. They are not peppy.' Mr. Putter himself has not been cute and peppy for a very long time''). At the animal shelter, however, he finds Tabby, a decidedly old yellow-and-white cat who needs a friend, too. In the second installment, quicker paced if less true to life, Mr. Putter and Tabby offer to take care of a neighbor's bulldog, Zeke, only to discover that Zeke isn't the darling ``little lollypup'' his owner believes him to be. Rylant's ( Missing May ; the Henry and Mudge series) texts, each broken into three short chapters, reflect admirable concern for brevity and meticulous consideration of every word. They are in perfect sync with Howard's expressive sketches, which slip abundant visual jokes into sunny, transparent watercolors and gouaches, and fluid pencil and pastel scribbles. Because the animals aren't strongly anthropomorphized, a sense of realism prevails, and the overall effect is sweet but never schmaltzy. Winsome and warmhearted, these books could become instant favorites. Ages 6-10. (Mar.)